dt-bindings: mfd: Update STM32 timers clock names

Clock name has been updated during driver/DT binding review:

  https://lkml.org/lkml/2016/12/13/718

Update DT binding doc to reflect this.

Fixes: 8f9359c6 (dt-bindings: mfd: Add bindings for STM32 Timers driver)
Signed-off-by: NFabrice Gasnier <fabrice.gasnier@st.com>
Acked-by: NBenjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/stm32-timers.txt

@@ -31,7 +31,7 @@ Example:
 		compatible = "st,stm32-timers";
 		reg = <0x40010000 0x400>;
 		clocks = <&rcc 0 160>;
-		clock-names = "clk_int";
+		clock-names = "int";
 
 		pwm {
 			compatible = "st,stm32-pwm";